Rifaximin crystalline forms and methods of preparation thereof

ABSTRACT

The present invention is directed to methods for preparation of a composition comprising mixed crystalline polymorphs rifaximin α and rifaximin β. For example, practice of a method of the invention can provide the composition comprising mixed crystalline polymorphs rifaximin α and rifaximin β wherein the rifaximin β is present in about 3-12% (w/w) or is present in about 5-8% (w/w). The composition comprising mixed crystalline polymorphs rifaximin α and rifaximin β is prepared by dissolving raw rifaximin in a water-soluble organic solvent, for example ethanol, at reflux, then adding water to achieve a final mixed solvent of about 7:3 (v/v) solvent to water ratio, then cooling to 35-40° C. until crystallization commences, then further cooling with stirring to 0° C., then recovery of the crystallized material, and drying to a water content of between 2.5% and 5.0%, to provide the composition comprising mixed crystalline polymorphs rifaximin α and rifaximin β. The composition is suitable for medicinal use, such as in treatment of infections of the gastrointestinal tract.

CLAIM OF PRIORITY

This application is a continuation of and claims the benefit of priorityto U.S. application Ser. No. 14/338,447, filed Jul. 23, 2014, whichclaims the benefit of priority of U.S. Provisional Patent ApplicationSer. No. 61/858,884, entitled “RIFAXIMIN CRYSTALLINE FORMS AND METHODSOF PREPARATION THEREOF,” filed on Jul. 26, 2013, the benefit of priorityof which is claimed hereby, and which is incorporated by referenceherein in its entirety.

BACKGROUND

Rifaximin is a semi-synthetic, non-systemic antibiotic that can bederived from rifamycin O by condensation with 2-amino-4-methylpyridine.Xifaxan® has Rifaximin as the active ingredient, and its labels arehereby incorporated by reference.

The U.S. Pat. No. 4,341,785, U.S. Pat. No. 4,557,866, U.S. Pat. No.7,045,620, U.S. Pat. No. 7,612,199, U.S. Pat. No. 7,902,206, U.S. Pat.No. 7,906,542, U.S. Pat. No. 7,928,115, U.S. Pat. No. 7,915,275, U.S.Pat. No. 7,923,553, U.S. Pat. No. 8,158,644, U.S. Pat. No. 8,158,781,and U.S. Pat. No. 8,193,196 provide methods for the synthesis ofpolymorphic forms of rifaximin and are hereby incorporated by referencein their entireties.

The U.S. Pat. No. 4,341,785 patent describes the preparation and use ofnew imidazo-rifamycin derivatives of a general formula which includesthe antibiotic rifaximin, having the structure

among the compounds claimed therein.

In U.S. Pat. No. 4,557,866, a process is described for conversion ofrifamycin O to rifaximin by contacting rifamycin O with2-amino-4-methylpyridine. The product was purified by crystallizationfrom ethanol/water 7:3.

The U.S. Pat. No. 7,045,620 describes crystalline polymorphous forms ofrifaximin, named rifaximin α and rifaximin β, and a poorly crystallineform named rifaximin γ. These forms were described as obtained by meansof a crystallization process carried out by hot-dissolving the rawrifaximin in ethyl alcohol and by causing the crystallization of theproduct by the addition of water at a determinate temperature and for adeterminate period of time. The crystallization was followed by dryingcarried out under controlled conditions until a specific water contentwas reached in the end product. The rifaximin α and rifaximin βcrystalline polymorphs were characterized by X-ray diffractogramproperties. It is described that the production of rifaximin α andrifaximin β during drying depends on the amount of water remaining atthe end, higher or lower than 4.5%, and not from the experimentalconditions of pressure and temperature at which this critical limit ofwater percentage is achieved. In fact, the two polymorphous forms, withhigher or lower water content, can be obtained by drying under vacuum orat atmospheric pressure, at room temperature or at high temperatures, inthe presence or in the absence of drying agents, provided that thedrying is conducted for the amount of time necessary so that the waterpercent characteristic for each polymorphous form is achieved. It isdescribed in the U.S. Pat. No. 7,045,620 patent that polymorphous formrifaximin β is obtained when the drying of the product, crystallized andwashed with water, is stopped at values of water higher than 4.5% andthat the polymorphous form rifaximin α is obtained by continuing thedrying until values lower than 4.5%, preferably between 2.0% and 3.0%,are reached. The polymorphous form rifaximin α, kept in an ambientenvironment with a relative humidity higher than 50% for a period oftime between 12 and 48 hours, turns into the polymorphous form β, whichin turn, by drying until an amount of water lower than 4.5% is reached,preferably comprised between 2.0% and 3.0%, turns back into thepolymorphous form rifaximin α.

In U.S. Pat. No. 7,612,199, it is disclosed that the polymorph calledrifaximin α is characterized by a water content lower than 4.5%,preferably between 2.0% and 3.0% and from a powder X-ray diffractogramwhich shows peaks at the values of the diffraction angles 2θ of 6.6°;7.4°; 7.9°; 8.8°; 10.5°; 11.1°; 11.8°; 12.9°; 17.6°; 18.5°; 19.7°;21.0°; 21.4°; 22.1°. The polymorph called rifaximin β is characterizedby a water content higher than 4.5%, preferably between 5.0% and 6.0%,and by a powder X-ray diffractogram which shows peaks at the values ofthe diffraction angles 2θ of 5.4°; 6.4°; 7.0°; 7.8°; 9.0°; 10.4°; 13.1°;14.4°; 17.1°; 17.90; 18.30; 20.9° The polymorph called rifaximin γ ischaracterized by a powder X-ray diffractogram much poorer because of thepoor crystallinity; the significant peaks are at the values of thediffraction angles 2θ of 5.0°; 7.1°; and 8.4°.

Crystal forms of rifaximin and their effect on pharmaceuticalproperties, are further described in Viscomi G C, et al, The RoyalSociety of Chemistry, CrystEngComm, 2008, 10, 1074-1081, which is herebyincorporated by reference in its entirety.

U.S. Pat. No. 8,158,781 and U.S. Pat. No. 8,158,644 claim the individualα, β, and γ crystalline polymorphs of rifaximin.

SUMMARY

The present invention is directed, in various embodiments, to methodsfor the manufacture of mixed crystalline polymorphs rifaximin α andrifaximin β.

In various embodiments, the invention can provide a method for themanufacture of a composition comprising mixed crystalline polymorphsrifaximin α and rifaximin β,

comprising

(a) dissolving rifaximin in a water-soluble organic solvent and warmingthe organic solvent to reflux; then, when the rifaximin is completelydissolved in the organic solvent to provide a solution of rifaximin inthe organic solvent,

(b) adding water to the solution to provide a second solution ofrifaximin in a mixed solvent, the mixed solvent having an organicsolvent to water ratio of about 5:5 to about 9:1 (v/v), to provide thesecond solution of rifaximin in the mixed solvent; then,

(c) cooling the second solution to a temperature of 25-50° C., andstirring at the temperature of 25-50° C. until crystallization takesplace, then

(d) cooling the solution to about 0° C. with stirring, then,

(e) recovering the crystallized material, then

(f) drying the crystallized material to a water content of between 2.5%and 5.0%;

to provide the composition comprising mixed crystalline polymorphsrifaximin α and rifaximin β.

In various embodiments, the composition can be a mixture of a majoritypercentage of the α rifaximin polymorph and a minority percentage of theβ rifaximin polymorph, preferably about 3% up to and including about 45%of the β rifaximin polymorph with the remainder being the α rifaximinpolymorph, more preferably about 3% up to and including about 30% of theβ rifaximin polymorph with the remainder being the α rifaximinpolymorph; especially more preferably about 3% up to and including about20% of the β rifaximin polymorph with the remainder being the αrifaximin polymorph; most preferably about 3-12% of the 0 polymorphmixed with a remainder of the α rifaximin polymorph; or especially mostpreferably the composition can be a mixture of about 5-8% of the βpolymorph mixed with a remainder of the α rifaximin polymorph.

By practicing a method of the invention as disclosed and claimed herein,a composition comprising mixed crystalline polymorphs of rifaximin canbe obtained rather than only a single crystalline polymorph. Thecomposition can be suitable for use in the formulation of medicaments,such as for the treatment of infections of the gastrointestinal (GI)tract.

A pharmaceutical composition useful as such a medicament can beformulated by combination of the Rifaximin mixed α and β polymorphs anda suitable pharmaceutical carrier. The percentage of α and β polymorphof the mixture can be any percentage given above. The pharmaceuticalcarrier includes those suitable for oral administration and preferablyready dissolution in the GI tract.

Xifaxan® has Rifaximin as the active ingredient, and its labels arehereby incorporated by reference.

DETAILED DESCRIPTION

A crystal polymorph or crystalline polymorph, as the term is usedherein, refers to each one of a plurality of crystalline forms that anorganic compound can assume in the solid state. As is well known in theart, the crystal form, i.e., as defined by the space group of thecrystal, is determined by the configuration of individual molecules ofthe compound that form the unit cell of the crystal. Often, solidsubstances will crystallize in one of several forms, and these variousforms are termed crystal polymorphs or crystalline polymorphs of thesubstance. The form a crystal of a compound will take uponcrystallization has been found in the art to be highly dependent uponthe conditions of crystallization, including solvent(s), temperature,time, agitation (stirring), rate of cooling, time of cooling, seeding,and the like.

A compound, when solid, can be composed of crystals of only one ofseveral possible polymorphs, or can be composed of mixtures of crystalsof different polymorphic forms. While typically each individual crystalis a single crystalline polymorphic form, it is also possible for solidforms of compounds to contain crystals or quasi-crystals composed ofcrystalline domains of more than a single polymorphic form.Alternatively, a sample that contains mixed polymorphic forms cancontain individual crystals each of a defined single polymorphic form,but the macroscopic sample comprising crystals of more than a singlepolymorphic form.

It is also well-known in the art that different crystalline polymorphsof an organic compound can display differing physical properties, suchas rate of dissolution, which can be important in the formulation of thecompound for use as a medicinal substance (medicament). Differentcrystalline polymorphs can thus have differing release profiles when themedicament is administered as a solid, and dissolution occurs in thegastrointestinal GI tract.

Rifaximin is used as a non-systemic antibiotic, as it is absorbed littleor not at all through the wall of the stomach or intestine whenadministered orally. As there is little or no uptake into the bloodstream when the antibiotic rifaximin is administered orally, for non-GIinfections is must be administered parenterally, and thus the mostprevalent use for rifaximin is in the treatment of GI conditions whereblood absorption is not required.

In the treatment of GI infections and the like, the rate of dissolutionof the solid rifaximin in the liquids of the GI tract is a significantfactor in determining the site and rate of passage of the antibioticinto solution, which is needed prior to any uptake by bacteria or thelike. The bacteria must absorb the antibiotic for the antibiotic to haveits lethal effect on the infective organisms.

The present invention is directed to methods for preparation of solidsamples of rifaximin wherein a mixture of crystalline polymorphs ispresent in the solid sample of rifaximin. In various embodiments, theinvention provides methods for conversion of “raw” or “residue”rifaximin, i.e., the molecular species as recovered from its preparation(e.g., from rifamycin O and 2-amino-4-methylpyridine), into a solidsample comprising a mixture of the rifaximin α and rifaximin βcrystalline polymorphic forms.

Accordingly, in various embodiments, the invention can provide a methodfor the manufacture of a composition comprising mixed crystallinepolymorphs rifaximin α and rifaximin β,

comprising

(a) dissolving rifaximin in a water-soluble organic solvent and warmingthe organic solvent to reflux; then, when the rifaximin is completelydissolved in the organic solvent to provide a solution of rifaximin inthe organic solvent,

(b) adding water to the solution to provide a second solution ofrifaximin in a mixed solvent, the mixed solvent having an organicsolvent to water ratio of about 5:5 to about 9:1 (v/v), to provide thesecond solution of rifaximin in the mixed solvent; then,

(c) cooling the second solution to a temperature of 25-50° C., andstirring at the temperature of 25-50° C. until crystallization takesplace, then

(d) cooling the solution to about 0° C. with stirring, then,

(e) recovering the crystallized material, then

(f) drying the crystallized material to a water content of between 2.5%and 5.0%;

to provide the composition comprising mixed crystalline polymorphsrifaximin α and rifaximin β.

For example, the organic solvent to water ratio can be about 7:3 (v/v).

For example, the cooling of the second solution can be to a temperatureof 35-40° C., and stirring at the temperature of 35-40° C. continueduntil crystallization takes place.

The term “water-soluble organic solvent” as used herein refers to asolvent that is soluble in water when in a mixed solvent having about70% (by volume) of the organic solvent and about 30% (by volume) water.For example, the water-soluble organic solvent can be an alcohol, suchas ethanol, or such as methanol, isopropanol, n-propanol,methoxyethanol, ethoxyethanol, and the like. Or, the water-solubleorganic solvent can be a ketone, such as acetone. or the water-solubleorganic solvent can be a water-soluble ether, such a dimethoxyethanol.Or, the water-soluble organic solvent can be a mixture, such as amixture of different alcohols, or a mixture of alcohols and ketones, oralcohols and ethers, or all together, and the like, provided that theorganic solvent and water are mutually soluble at a ratio of about 7:3(v/v) solvent to water (v/v).

The composition comprising mixed crystalline polymorphs rifaximin α andrifaximin β can comprise various ratios of the two polymorphiccrystalline forms rifaximin α and rifaximin β. For example, thecomposition obtained by practice of a method of the invention cancomprise mixed crystalline polymorphs rifaximin α and rifaximin βwherein a majority percentage of the mixture is the α polymorph with aminority percentage being the 0 polymorph. Preferably the mixture can beabout 3% up to 45% 0 polymorph with the remaining percentage being the αpolymorph. More preferably, the mixture can be about 3% up to about 30%0 with the remaining percentage of the mixture being α. Especially morepreferably, the mixture can be about 3% up to about 20% 0 with theremaining percentage being α. Most preferably, the mixture can be about3-12% (w/w) of the rifaximin β crystalline polymorph in mixture with theremaining percentage of the rifaximin α crystalline polymorph.Especially most preferably, the composition comprising mixed crystallinepolymorphs rifaximin α and rifaximin β can contain about 5-8% (w/w) ofthe rifaximin β crystalline polymorph in the mixture with the rifaximinα crystalline polymorph, in the solid composition that is obtained bypractice of an embodiment of the method disclosed and claimed herein.

In various embodiments of the inventive method, a sample of rifaximin,e.g., of purity suitable for use in administration to a patient in needthereof or in formulation of a medicament for administration to apatient in need thereof, is dissolved in the water-soluble organicsolvent. This starting sample of rifaximin can be obtained by thesemi-synthetic conversion of, e.g., rifamycin O, obtainable from natural(fermentation) sources, to rifaximin by reaction with2-amino-4-methylpyridine (2-amino-γ-picoline), under conditionsoptionally further comprising iodine, as outlined in the syntheticprocedures provided in the Examples, below.

Any sample of rifaximin of suitable chemical purity for pharmaceuticaluse can be employed. The first step of the inventive method is:

(a) dissolving rifaximin in a water-soluble organic solvent and warmingthe organic solvent to reflux and when the rifaximin is completelydissolved in the organic solvent to provide a solution of rifaximin inthe organic solvent.

The refluxing and dissolving of the rifaximin can be carried out in anymethod known to the person of skill in the art, i.e., in a round-bottomflask or a large-scale reactor, fitted with a reflux condenser, stirringmeans, and means for subsequent addition of water to the hot, refluxingsolution of rifaximin. Typically, on a larger scale, stirring isaccomplished by means of an overhead stirrer fitted with a paddle andshaft of non-reactive materials, i.e. Teflon or stainless steel paddleand glass or metal shaft. The reflux condenser can be of any suitableconstruction. The dissolution step can be carried out under inert gas,e.g., nitrogen or argon atmosphere, or can be carried out under ambientatmospheric conditions.

As noted above, the solvent can be an alcohol, such as ethanol,methanol, isopropanol, n-propanol, methoxyethanol, ethoxyethanol, or thelike, or can be a ketone such as acetone, or can be a water-solubleether such as dimethoxyethanol, etc.

The determination that dissolution of the rifaximin has taken place,i.e., that solution is complete, can be made visually, e.g., using asight tube on a reactor, or simply viewing the contents of a glassflask, or can be made using standard optical equipment to measure %transmittance or the like. Complete solution of the rifaximin is neededprior to addition of water in the second step. If insoluble materialsother than rifaximin are present, it is possible to remove them byfiltration prior to addition of the water.

In the second step, the clear solution of rifaximin in the organicsolvent is kept at the temperature at or near reflux, then:

(b) adding water to the solution to provide a second solution ofrifaximin in a mixed solvent, the mixed solvent having an organicsolvent to water ratio of about 7:3 (v/v), to provide the secondsolution of rifaximin in the mixed solvent.

This step can be carried out in the same flask or reactor that was usedto dissolve the rifaximin in the water-soluble organic solvent. Watercan be added over a period of time, such as about 30 minutes, whilemaintaining the warm temperature at or near the reflux point of theorganic solvent. Any suitable apparatus, such as an addition funnel ortube, can be used that is compatible with the vessel and the refluxcondenser setup. Water can be added dropwise with stirring, to avoidlocal high concentrations of water that could results in prematureprecipitation of solid rifaximin, prior to the desired step ofcrystallization. Water addition is continued until a volume to volume(v/v) ratio of about 7 parts organic solvent and about 3 parts water isachieved, providing the second solution comprising rifaximin in theaqueous organic solvent mixture.

After the target ratio of organic solvent and water is reached, thesolution should still be complete at the elevated temperature, i.e.,premature precipitation of the rifaximin should not have taken place. Itis within ordinary skill to adjust total volumes of solvent and water torifaximin to provide a second solution wherein the rifaximin is fullydissolved at elevated temperatures, but is concentrated enough thatcrystallization begins to occur upon cooling to the temperature of35-40° C. Thus, the next steps of the inventive process are:

(c) cooling the second solution to a temperature of 35-40° C., andstirring at the temperature of 35-40° C. until crystallization takesplace, then

(d) cooling the solution to about 0° C. with stirring, untilcrystallized material is present.

As the mixed aqueous organic solvent and dissolved rifaximin are cooled,with stirring, to the temperature of 35-40° C., crystallization beginsto take place. Seeding is not necessary. The selection of an appropriateconcentration of the rifaximin in the mixed solvent can be determined byroutine experimentation, such that the solution is sufficientlyconcentrated that no rifaximin has precipitated at the refluxtemperature, but crystallization begins to occur at the 35-40° C.temperature. The heating of the flask or reactor in which this processis carried out is regulated by means well known in the art, e.g.,thermostated oil bath, electrical heating units, and the like. While thefirst step of the process at reflux does not need close regulation ofthe thermal input, as the temperature of the solution is self-regulatedby the reflux process, the step of cooling from reflux to the 35-40° C.temperature requires accurate thermal regulation, as with a thermostat.Stirring can be carried out by any of the means well-known in the art,such as with the paddle-type overhead stirrer described above. Stirringcontinues as the reaction is cooled and held at the 35-40° C.temperature. When crystallization is observed to have initiated, e.g.,by visual inspection or optical device, heating is discontinued, butstirring is continued, and the solution is cooled to about 0° C., and iscontinued as the composition containing the crystallizing rifaximin ischilled.

When crystallization has progressed to a satisfactory degree, and isbelieved to be sufficiently complete for the effective recovery of therifaximin active ingredient, a valuable material, the crystallizedmaterial is recovered by any means known in the art, e.g., filtration,centrifugation, or the like. Thus, the process involves:

(e) recovering the crystallized material, then

(f) drying the crystallized material to a water content of between 2.5%and 5.0%;

to provide the composition comprising mixed crystalline polymorphsrifaximin α and rifaximin β.

Once the crystallized material has been recovered, it is dried to aknown level of water content, of between 2.5% and 5.0%. Water content ofthe solid can be determined by methods known in the art, such as KarlFischer titration. It is also possible to obtain X-ray powderdiffractograms of the material, which serves to indicate the relativecontents of the rifaximin α and rifaximin β polymorphs in the finalproduct. Other rifaximin polymorphs can also be present, but thepredominant polymorphs are the rifaximin α and rifaximin β polymorphs.It is possible that a certain amount of the relatively amorphousrifaximin γ can also be present. As discussed above, a content of abouta minority percentage of rifaximin β, or a content of up to 45%, up to30%, up to 20%, about 3-12% or about 5-8% rifaximin β, with a remainingpercentage of rifaximin α can be present in the composition comprisingmixed crystalline polymorphs rifaximin α and rifaximin β, obtained bypractice of a method of the present invention. The majority remainder ofthe composition can be rifaximin α. The relative proportions can bedetermined from the X-ray powder diffractograms; the characteristic 2θdiffraction angles are provided in the patent documents cited above,which are incorporated by reference herein in their entireties. Inparticular, an XRPD pattern showing 2θ absorptions as a doublet at 7.4°and 7.9° as indicative of the α polymorph and 2θ absorptions as asinglet at 5.4° and a triplet at 10.5°, 11.1° and 11.8° as indicative ofthe β polymorph will indicate the mixed crystals of α and β polymorphs.The full XRPD pattern of the mixed polymorph will also presentoverlapping and unique 2θ absorptions of the combined XRPD patterns ofthese two polymorphs.

Drying can be carried out by any of the methods well-known in the art,e.g., under vacuum or in a dry atmosphere, over an absorbent such asanhydrous sodium or magnesium sulfate, and the like. Warming is notnecessary, and excessive warming is to be avoided.

When the water content of the solid reaches the level of between 2.5%and 5.0%, inspection of the X-ray powder diffractogram of the sample canreveal that a mixture of rifaximin α and rifaximin β has been obtained,possible comprising additional crystalline polymorphs. This mixture ofpolymorphs can be suitable for use in administration to a patient or informulation of a medicament suitable for oral administration. It iswithin routine skill to evaluate the dissolution parameters of a samplehaving a defined composition prepared by an embodiment of a method ofthe invention.

Selection of the organic solvent, the ratio of organic solvent to water,the temperature and time of initial cooling and commencement ofcrystallization, and the temperature and time of final cooling andcollection of the crystallized material can all be determined by theperson of ordinary skill using the disclosed subject matter herein inconjunction with ordinary knowledge and routine optimization. The use ofdifferent organic solvents can result in changes in optimal solvent towater ratios, temperatures, and concentrations of rifaximin in theliquid milieu. Determination of recoveries of the composition comprisingthe mixture of rifaximin α and rifaximin β using various conditions caninform the selection of the optimized parameters by the ordinarypractitioner.

Similarly, it is within ordinary skill, monitoring the drying processand the ratio of the rifaximin α and rifaximin β in the product byprocess as disclosed and claimed herein, to obtain a compositionsuitable for a particular formulation for the rifaximin medicament.

EXAMPLES Example 1 Preparation of Rifaximin Residue Example 1A

A sample of 75.4 Grams (0.1 moles) of rifamycin O and 32.4 g (0.3 moles)of 2-amino-4-methyl-pyridine is dissolved in 400 ml of methylenechloride and the obtained solution kept at room temperature for 48hours. After washing the reaction mixture first with 600 ml of anaqueous 1N solution of hydrochloric acid and then with water, and dryingthe organic phase over sodium sulfate, the methylene chloride waseliminated by evaporation under vacuum that forms a residue ofrifaximin.

Example 1B

A solution of 34.7 g (0.046 moles) of rifamycin O, 14.9 g (0.138 moles)of 2-amino-4-methyl-pyridine and 2.8 g (0.011 moles) of iodine in 200 mlof methylene chloride is kept at room temperature for 24 hours. Afteradding 20 ml of an aqueous 20% solution of ascorbic acid and stirringfor 30 minutes, the reaction mixture is first washed with 400 ml of anaqueous 1N solution of hydrochloric acid and then with water toneutrality. The organic phase is recovered, dried over sodium sulfateand the solvent is evaporated under vacuum.

Example 1C

A sample of 34.7 Grams (0.046 moles) of rifamycin O, 14.9 g (0.138moles) of 2-amino-4-methyl-pyridine and 2.8 g (0.011 moles) of iodine isdissolved in 150 ml of a 7/3 (v/v) mixture of ethanol/water. Theresulting solution is stirred for 18 hours at room temperature, then 2.8g of iodine added and stirring continued for further 2 hours. Thereaction mixture is mixed with 5.3 g (0.03 moles) of ascorbic acid andleft to stand for 2 days at a temperature of about 5° C.

Example 1D

As ample of 200 Grams (0.265 moles) of rifamycin O and 65.5 g (0.607moles) of 2-amino-4-methyl-pyridine is dissolved in 1000 ml of methylenechloride and is kept at room temperature for 40 hours. The reactionmixture is washed with 900 ml of an aqueous 1N solution of hydrochloricacid and then with water to neutrality. The washing liquors are castoff, the organic layer dried over sodium sulfate and the productobtained after evaporating the solvent under vacuum.

Example 1E

A sample of 200 Grams (0.265 moles) of rifamycin O and 65.5 g (0.607moles) of 2-amino-4-methyl-pyridine is dissolved in 1000 ml of methylenechloride and kept at room temperature for 20 hours in presence of 11 g(0.043 moles) of iodine. Treatment with 130 ml of aqueous 20% solutionof ascorbic acid yields the final residue.

Example 1F

A sample of 100 Grams (0.132 moles) of rifamycin O and 57.1 g (0.528moles) of 2-amino-4-methyl-pyridine is stirred in 400 ml of a 1:1 (v/v)mixture of ethanol/water at room temperature for 20 hours. The obtainedsolid is washed with a 1:1 (v/v) mixture of ethanol/water and then driedunder vacuum.

Example 1G

A sample of 60 Grams (0.08 moles) of rifamycin O and 32.4 g of2-amino-4-methyl-pyridine is stirred in 120 ml of a 9:1 (v/v) mixture ofpropylene glycol/ethanol for 18 hours at room temperature and theobtained mixture is left standing for 72 hours. After diluting with 160ml of a 1:1 (v/v) mixture of 2N aqueous hydrochloric acid/ethanol thereaction mixture is filtered, and the residue collected.

Example 1H

A sample of 100 Grams (0.13 moles) of rifamycin O and 43.3 g (0.39moles) of 2-amino-4-methyl-pyridine is stirred in 300 ml of a 3:2 (v:v)mixture of isopropanol/water for 16 hours at room temperature. Thereaction mixture is subsequently filtered, the solid is washed with thesame mixture of solvents used in the reaction and dried under vacuum.

Example 1I

A sample of 100 Grams (0.13 moles) of rifamycin O and 43.3 g (0.39moles) of 2-amino-4-methyl-pyridine is stirred in 300 ml of a 3:2 (v:v)mixture of tert.-butanol/water for 16 hours at room temperature. Thereaction mixture is subsequently filtered, and the solid washed with thesame mixture of solvents used in the reaction and dried under vacuum.

Example 2 Crystallization of Rifaximin According to Methods of theInvention Example 2A

Rifaximin residue obtained, e.g., by any of the above methods, is takeninto 80 mL of Ethanol solution and transfer into a 3 necked RB flaskstir for 10 mins. The temperature is increased to 70° C. to the refluxtemperature of ethanol, and the solution stirred for completedissolution. Then 30 mL of water are added over a time period of 30minutes. The solution is then cooled to 35-40° C., then stir for 30minutes, and observed for crystallization. Once crystallization hasbegun, the solution is furthered cool to 0° C. and stirred for 4 hrsuntil complete crystallization has taken place.

Example 2B

Employing the same molar ratio of the solvents as in Example 2A, theresidue is taken into methanol solution under the same reactionconditions to obtain the desired product.

Example 2C

Employing the same molar ratio of the solvents as in Example 2A, theresidue is taken into n-propanol solution under the same reactionconditions to obtain the desired product.

Example 2D

Rifaximin residue is mixed into 80 mL of acetone and transferred into a3 necked RB flask, stirring for 10 mins. The temperature is raised toreflux and the solution stirred until complete dissolution occurs. Then30 mL of water is added over a time period of 30 minutes. The solutionis cooled to 35-40° C., and stirred for 30 minutes, observingcrystallization. After crystallization has begun, the solution isfurther cooled to 0° C., stirring for 4 hrs until completecrystallization has occurred. Then the product is filtered and washedwith 100 mL water.

Example 3 Drying of Rifaximin to Provide the Composition ComprisingMixed Crystalline Polymorphs Rifaximin α and Rifaximin β

A crystallized sample, recovered from the aqueous organic mixedcrystallization solvent, e.g., as outlined in any of Examples 2A-2D, isplaced in a suitable container, tray, or the like, and placed undercondition for drying, i.e., evaporative removal of the organic solvent,and of the water down to the specified content of between 2.5% and 5.0%by weight, as determined, e.g., by Karl Fischer titration, proton NMR,or other methods well known in the art. Drying can be assisted bypartial or complete vacuum, by a stream of dry gas (e.g., nitrogen), andaided by the presence of a water absorbent such as anhydrous sodium ormagnesium sulfate. The proportion of the rifaximin β and the rifaximin αin the composition comprising mixed crystalline polymorphs rifaximin αand rifaximin β is readily determined by X-ray powder diffraction, as iswell-known in the art and is described in the patent documents cited andincorporated by reference herein.

Formulations

Another aspect of an embodiment of the invention provides compositionsof the compounds of the invention, alone or in combination with anothermedicament. As set forth herein, compounds of the invention includestereoisomers, tautomers, solvates, prodrugs, pharmaceuticallyacceptable salts and mixtures thereof. Compositions containing acompound of the invention can be prepared by conventional techniques,e.g. as described in Remington: The Science and Practice of Pharmacy,19th Ed., 1995, or later versions thereof, incorporated by referenceherein. The compositions can appear in conventional forms, for examplecapsules, tablets, solutions, or suspensions.

Typical compositions include a compound of the invention and apharmaceutically acceptable excipient which can be a carrier or adiluent. For example, the active compound will usually be mixed with acarrier, or diluted by a carrier, or enclosed within a carrier which canbe in the form of an ampoule, capsule, sachet, paper, or othercontainer. When the active compound is mixed with a carrier, or when thecarrier serves as a diluent, it can be solid, semi-solid, or liquidmaterial that acts as a vehicle, excipient, or medium for the activecompound. The active compound can be adsorbed on a granular solidcarrier, for example contained in a sachet. Some examples of suitablecarriers are water, salt solutions, alcohols, polyethylene glycols,polyhydroxyethoxylated castor oil, peanut oil, olive oil, gelatin,lactose, terra alba, sucrose, dextrin, magnesium carbonate, sugar,cyclodextrin, amylose, magnesium stearate, talc, gelatin, agar, pectin,acacia, stearic acid or lower alkyl ethers of cellulose, silicic acid,fatty acids, fatty acid amines, fatty acid monoglycerides anddiglycerides, pentaerythritol fatty acid esters, polyoxyethylene,hydroxymethylcellulose and polyvinylpyrrolidone. Similarly, the carrieror diluent can include any sustained release material known in the art,such as glyceryl monostearate or glyceryl distearate, alone or mixedwith a wax.

The formulations can be mixed with auxiliary agents which do notdeleteriously react with the active compounds. Such additives caninclude wetting agents, emulsifying and suspending agents, salt forinfluencing osmotic pressure, buffers and/or coloring substancespreserving agents, sweetening agents or flavoring agents. Thecompositions can also be sterilized if desired.

The route of administration can be any oral route which effectivelytransports the active compound of the invention to the appropriate ordesired site of action.

If a solid carrier is used for oral administration, the preparation canbe tableted, placed in a hard gelatin capsule in powder or pellet formor it can be in the form of a troche or lozenge. If a liquid carrier isused, the preparation can be in the form of a syrup, emulsion, softgelatin capsule.

The formulations of the invention can be designed to provide quick,sustained, or delayed release of the active ingredient afteradministration to the patient by employing procedures well known in theart. Thus, the formulations can also be formulated for controlledrelease or for slow release.

Compositions contemplated by the present invention can include, forexample, micelles or liposomes, or some other encapsulated form, or canbe administered in an extended release form to provide a prolongedstorage and/or delivery effect.

Tablets, dragees, or capsules having talc and/or a carbohydrate carrieror binder or the like are particularly suitable for oral application.Preferable carriers for tablets, dragees, or capsules include lactose,corn starch, and/or potato starch. A syrup or elixir can be used incases where a sweetened vehicle can be employed.

A typical tablet that can be prepared by conventional tabletingtechniques can contain:

Core: Active compound (as free compound or salt thereof) 250 mg Colloidal silicon dioxide (Aerosil ®) 1.5 mg Cellulose, microcryst.(Avicel ®)  70 mg Modified cellulose gum (Ac-Di-Sol ®) 7.5 mg Magnesiumstearate Ad. Coating: HPMC approx.   9 mg *Mywacett 9-40 T approx. 0.9mg *Acylated monoglyceride used as plasticizer for film coating.

A typical capsule for oral administration contains compounds of theinvention (250 mg), lactose (75 mg) and magnesium stearate (15 mg). Themixture is passed through a 60 mesh sieve and packed into a No. 1gelatin capsule.

All patents and publications referred to herein are incorporated byreference herein to the same extent as if each individual publicationwas specifically and individually indicated to be incorporated byreference in its entirety.

The terms and expressions which have been employed are used as terms ofdescription and not of limitation, and there is no intention that in theuse of such terms and expressions of excluding any equivalents of thefeatures shown and described or portions thereof, but it is recognizedthat various modifications are possible within the scope of theinvention claimed. Thus, it should be understood that although thepresent invention has been specifically disclosed by preferredembodiments and optional features, modification and variation of theconcepts herein disclosed may be resorted to by those skilled in theart, and that such modifications and variations are considered to bewithin the scope of this invention as defined by the appended claims.

What is claimed is:
 1. A rifaximin composition comprising mixedcrystalline polymorphs rifaximin α and rifaximin β containing about3-12% (w/w) of the rifaximin β crystalline polymorph in mixture with aremaining percentage of the rifaximin α crystalline polymorph.
 2. Therifaximin composition of claim 1 wherein rifaximin β is present in about5-8% (w/w).
 3. The rifaximin composition of claim 1 further containingfrom about 2.5% to about 5% by weight water relative to the weight ofthe total composition.
 4. A pharmaceutical composition for oraladministration comprising an effective amount of a rifaximin compositionof claim 1 and a pharmaceutically acceptable carrier.
 5. Thepharmaceutical composition according to claim 4 for treatment ofgastrointestinal malconditions.
 6. The pharmaceutical compositionaccording to claim 4 in unit dosage form.
 7. The pharmaceuticalcomposition according to claim 6 wherein the unit dosage form is atablet.
 8. The pharmaceutical composition according to claim 7 whereinthe unit dosage form contains about 250 mg of rifaximin.
 9. Thepharmaceutical composition according to claim 8 wherein the unit dosageform includes a pharmaceutically acceptable carrier.
 10. Thepharmaceutical composition according to claim 9 wherein the carrier is asolid diluent.
 11. The pharmaceutical composition according to claim 9wherein the composition is in the form of particles contained in agelatin capsule.